An endoscope is used to inspect body cavities, such as the colon, intestines, esophagus, etc. An elongate distal tubular insertion section of an instrument body carrying an imaging optical system and an illumination optical system. The insertion portion is inserted into and traverses through the body cavity to a target of particular interest. For the sake of ease and to reduce pain to the patient, the insertion portion should be as flexible as possible and allow control by the remote user, while still allowing illumination to be carried to the tip of the insertion portion and allowing image data to be transmitted therefrom. In addition, the tubular insertion portion must be made from a biocompatible material.
A prior art insertion tube is known and described in U.S. Pat. No. 3,670,721, issued to Fukami et al. In the instant reference, an insertion tube includes a thin metal section wound into a spiral tubular configuration and a net-like braid which is placed in overlaying relationship onto the length of the spiral tube. A molten layer of a synthetic resin or synthetic rubber is embedded into the braid, and subsequent molten layers can be added to existing layers to improve the handling characteristics of the tube. The described tube provides a reasonable amount of flexibility, but the molten layer is caused to penetrate into the braid, thereby degrading the overall elasticity of the tube.
In U.S. Pat. No. 4,753,222, to Morishita, an insertion tube is described, also having a similar spiral tube and a net-like braid placed in overlaying relation. According to this patent, an inner or intermediate tubular member made from a high-polymer material is then force-fitted over the outer periphery of the braid and a second or outer tubular member is formed by applying a molten high-polymer material onto the outer surface of the inner tubular member via a molding process or a die assembly process. The intermediate tubular member isolates the braid and spiral tube from the molten polymer material and therefore prevents deterioration of the restoration force of the braid and spiral tube.
While this tube provides additional advantages, it would appear that the instant tube, and particularly the desired force or interference fit of the intermediate layer relative to the braid and the spiral tube, is difficult to manufacture.
Another problem relates to the range markings found commonly on endoscopic insertion tubes. The markings are printed or otherwise applied to the outer surface of the tube and provide a guide as to the depth of penetration of the tube into the body cavity of interest. Because the outer surface of the tube must be biocompatible, it has been difficult to preserve the markings during the life of the insertion tube. Consequently, tubes must often be replaced before the useful life of the tube itself due to premature fading of the markings.